It will be remembered that Ney had been entrusted by Napoleon with the absolute and independent command of something less than half of his whole army.[7] He had put at his disposal the First and the Second Army Corps, under Erlon and Reille respectively--nearly 46,000 men; and to these he had added, by an afterthought, eight regiments of heavy cavalry, commanded by Kellerman. The rôle of this force, in Napoleon's intention, was simply to advance up the Brussels road, brushing before it towards the left or west, away from the Prussians, as it went, the outposts of that western half of the allied army, which Wellington commanded. We have seen that Napoleon, who had certainly arrived quickly and half-unexpectedly at the point of junction between Wellington's scattered forces and those of the Prussians, when he crossed the Sambre at Charleroi, overestimated his success. He thought his enemy had even less notice of his advance than that enemy really had; he thought that enemy had had less time to concentrate than he had really had. Napoleon therefore necessarily concluded that his enemy had concentrated to a less extent than he actually had. That mistake had the effect, in the case of the army of the right, which he himself commanded, of bringing him up against not one Prussian army corps but three. This accident had not disconcerted him, for he hoped to turn it into a general disaster for the Prussians, and to take advantage of their unexpected concentration to accomplish their total ruin. But such a plan was dependent upon the left-hand or western army, that upon the Brussels road under Ney, not finding anything serious in front of it. Ney could spare men less easily if the Emperor's calculation of the resistance likely to be found on the Brussels road should be wrong. It was wrong. That resistance was not slight but considerable, and Ney was not free to come to Napoleon's aid. Tardy as had been the information conveyed to the Duke of Wellington, and grievously as the Duke of Wellington had misunderstood its importance, there was more in front of Ney upon the Brussels road than the Emperor had expected. What there was, however, might have been pushed back--after fairly heavy fighting it is true, but without any risk of failure--but for another factor in the situation, which was Ney's own misjudgment and inertia.